Catalyst entrained in the effluent from a thermal unit operation, such as fluidized catalytic cracking (FCC) of petroleum gas oil, may be recovered for re-use. Various separation units are known for separating solids from hot gases. Continuously operated fluidized bed systems often employ primary or secondary cyclones for the main separation operations; however, these units often permit a small, but significantly costly, amount of valuable catalyst to escape the system by entrainment in the effluent gas. For example, in continuous cyclic FCC systems, an oxidative regeneration step is required to remove coke deposits from zeolite particles, usually having a particle size range from 1 to 150 microns, typically 20 to 100 microns average size.
The regeneration usually involves high temperature burning of the carbonaceous deposits to generate a flue gas having a temperature of about 600.degree. to 800.degree. C. While the major amount of regenerated catalyst is readily recovered from the hot flue gas by primary and secondary cyclone devices, filters, etc., a minor amount of the fine particles, typically having a particle size less than 40 microns, is entrained in the flue gas.
In order to utilize the flue gas safely in downstream energy recovery units, such as turbines, etc., and to avoid expensive catalyst make-up requirements, it is desirable to recover the entrained solids more completely. Accordingly, an auxiliary or tertiary recovery unit can be employed for this purpose. Such a downstream separator must be able to withstand the erosion of high-velocity, particle-laden gases and the thermal expansion and contraction due to dynamic changes in the gas streams being cleaned.
Intermittent or cyclic changes in thermal conditions can occur during FCC process startup or upset conditions. Fluctuation in the flue gas temperature must be accommodated by the downstream separator and the materials of construction require adaptation to dimensional changes of the materials employed, usually base metals, such as carbon steel and refractory oxides.
It is an object of the present invention to prevent excessive damage to a recovery unit for solids-gas separation which is caused by differential thermal expansion between the various components when the unit is in operation. A technique has been found for operating a solids-gas separator under dynamic temperature conditions to permit differential expansion of internal components relative to the unit shell by providing a vertically slidable, adjustable sealing mechanism in the bottom outlet portion of the separator.